Patent GB-757882-A (GB)
Title: Electron discharge apparatus
Inventor: O'NEILL GEORGE DEAN
IPC: H01J25/76
Filed: 1951-02-08
Abstract: 757,882. Discharge apparatus. SYLVANIA ELECTRIC PRODUCTS, Inc. Feb. 8, 1951, No. 3145/51. Class 39 (1). Electric discharge apparatus includes a cavity resonator 17, Fig. 2, adapted to have high-frequency oscillations generated therein, and for use as a detector or modulator, a first electrode 1 for emitting electrons, an apertured second electrode 2 for attracting electrons from the first electrode 1 and for passing the electrons towards a third electrode 3, the surface of which emits a greater number of secondary electrons than the bombarding electrons, means 8, 14, 15 for applying to the second and third electrodes 2 and 3 potentials which are positive relative to the potential of the first electrode 1, and such that the current of the third electrode 3 decreases with increases in voltage on the third electrode 3 over an operating range and means 13, 16, 16a, 17, 18, 19 for coupling the second and third electrodes 2 and 3 to the cavity resonator 17. The potential applied to the second electrode 2 may be higher than that applied to the third electrode 3. The cavity resonator 17 is screwed to the threaded end 16a of the rod 16 carrying the third electrode 3. The discs 13 and 18 connected to the second grid electrode 2 are separated from the resonator 17 by a disc 19 of dielectric material which forms a direct-current breach and a by-pass capacitor which offers negligible impedance to the very high-frequency alternating current generated but isolates the grid 2 from the electrode 3 as far as direct current is concerned. The dimensions of the capacitor are chosen so that there will be substantially no radiation of the electromagnetic oscillations occurring inside the resonator 17. Oscillatory power may be abstracted, or signals to be detected may be injected through a loop 20 coupling the resonator to a coaxial transmission line 21. The electrodes 2 and 3 are convex towards the cathode 1 as shown to minimize accumulation of electrons from electrode 3 in space between electrodes 1 and 2. The cathode 1 may be indirectly heated as shown in Fig. 2 or directly heated as shown in Figs. 3 and 4. The cathode shown in Figs. 3 and 4 comprises an assembly supported on a mica disc 22 mounted on pins 23, 24 and 25. The ends of a filament wire 26 are welded to tabs 27 and 28 and tension is applied to wire 26 by a spring 29 attached to pin 24. Slots 30 and 31 in the mica disc 22 guide the filament from pin 23 to the tension spring and to the pin 25, the filament twice passing over a central aperture 32 in the disc, coatings 33 and 34 being applied to the filament in this region. In the construction shown in Fig. 9, the resonator 17 is directly connected to the grid disc 13 and the direct current supply may be connected directly to an external portion of the resonator and through an impedance to an antenna extension 12 of the rod 16. Alternatively the direct current connectors and by-pass capacitor of Fig. 2 can be used. The antenna extension 12 passes through a hole in the top of the resonator and is rigid with a disc 34 which forms with the top of the resonator a capacitive coupling between the resonator 17 and the rod 16. The resonator can be surrounded with a slot 37 one-quarter wave length long and bounded by a cylindrical wall 38. In the construction shown in Fig. 10 the resonator is coupled to a transmission line 21 and a transmission line 35 is tapped into the transmission line 21 for the supply of positive voltage. The line 35 may be left open at its outer end and may be one-quarter wave length long so as to present zero impedance at its inner end. The line 21 terminates in a device having substantially zero conductance unless the by-pass arrangement 18 and 19 of Fig. 2 is used. A modulated signal may be obtained by including a beam-focusing electrode or a control grid adjacent the cathode.